Silver (Ag) foils are bonded to alumina substrates by a low temperature solid state bonding process. The alumina substrate is premetalized with 40 nm titanium tungsten (TiW) and 2.54 μm gold (Au). The bonding temperature is just 260 °C, compatible with the peak reflow temperature of lead-free (Pb-free) solders used in electronic industries. The Ag foil is quite soft and ductile. It can deform to mate with the Au surface on alumina. Thus, only 1000 psi of static pressure is needed to bring Ag atoms and Au atoms within atomic distance on the interface. Ag has superior physical properties. It has the highest electrical and thermal conductivities among the metals. Scanning electron microscope (SEM) images show that the Ag foil is well bonded to the Au layer on alumina. A standard shear test is performed to determine the shear strength of the bonding. The shear strength of five samples tested far exceeds the strength requirement of MIL-STD-883 G standard.

Issue Section:
Research Papers
Keywords:
alumina, bonding processes, deformation, foils, gold, scanning electron microscopy, shear strength, silver, solders, titanium compounds, fluxless bonding, solid state bonding, silver, alumina
Topics:
Bonding, Diffusion bonding (Metals), Pressure, Silver, Shear (Mechanics), Shear strength, Solders, Atoms, Temperature

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Available online: http://www.q-tech.com/assets/tests/std883_2019.pdf
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